In general, maps are figures in which a part or all of the earth's surface is expressed on a plane with a reduced scale, and seas, mountains, streams, land, etc. are expressed using various symbols, characters, colors, etc. Examples of the maps include topographical maps, land registration maps, etc. The reduced scale is a ratio of a distance on a map with respect to a real distance corresponding to the distance on the map. For example, the reduced scale can be expressed as of 1:100,000 or 1/100,000, which means that a real distance is represented on a map by a distance equal to 1/100,000 of the real distance. The reduced scale can be different depending upon the map used and is generally displayed at an upper or lower end of the map. The accuracy of a map is proportional to the reduced scale of the map.
Maps can be used for various purposes such as searching for paths or desired places, observing topographies, calculating areas of regions, etc. Among the various purposes, maps are frequently used for calculating a distance of a road connecting two real positions or a direct distance between two positions. That is, maps are used for calculating a distance that must be traveled to get from a position to another position.
Conventionally, troublesome procedures must be performed to obtain a real distance of a real path connecting two real positions using a map. That is, in order to obtain a real distance of a real path, first, a first point and a second point corresponding to the two real positions are chosen. Then, when the map path connecting the first point and the second point is linear, the map distance can be obtained using a ruler. When the map path connecting the first point and the second point is curved, the map distance can be obtained by attaching a wet thread to the map along the map path, detaching the wet thread from the map, stretching the wet thread straight, and then measuring the length of the wet thread corresponding to the map path using a ruler. The map distance may also be obtained using an opisometer. The real distance is calculated by multiplying the obtained map distance by the reduced scale displayed on the map.
Even when using the opisometer, it is very inconvenient to obtain the real distance using the above method, and it may be impossible to obtain a real distance corresponding to a continuously curved path using the above method.